Examples of chewing gums in compressed form produced by direct compression of mixtures in powder form have been known in the art for several years and various types are available commercially. However, the compressed-powder gums which are currently available are unpleasant to chew because to avoid technical difficulties in the production process they have been produced from hard basic gums. It is in fact known that it is much easier to grind and compress hard and dry materials and that the compression of powders is more complex the softer they are; up to now, the need to have starting mixtures or materials which are sufficiently hard or dry to be granulated and compressed easily has led to the production of chewing gums which are hard and friable, with the risk of some of the gum accidentally being swallowed.
Various chewing gums produced by the compression of powdered ingredients are described in the literature. As early as 1942, U.S. Pat. No. 2,290,120 described, for example, the preparation of chewing gums by cold grinding of basic gum and glucose syrup (at about −20° C.) and subsequent mixing and compression thereof; however, the basic gums used in this patent contain natural gums which, owing to their known limitations with regard to performance, quality of supply, and technical problems of use, have now been almost completely abandoned and replaced by other, synthetic ingredients.
U.S. Pat. No. 4,753,805 describes the granulation and subsequent compression of a chewing-gum composition having a moisture percentage of between 2 and 8%, with the use of various technological coadjuvants such as anti-agglutination agents and granulation coadjuvants (alkali-metal phosphates, alkaline-earth metal phosphates, maltodextrins, or mixtures thereof).
European patent EP-0221850 describes chewing-gum formulations which are suitable for being formed into tablets and which are produced by mixing the basic gum with dry ingredients, including the aromatic portion, without the plasticization due to the oils of the flavourings, subsequent cooling of the mixture to above the freezing point of water (5-10° C.), dry granulation, and compression.
U.S. Pat. No. 4,000,321 describes a chewing gum with characteristics of softness during chewing and light weight. This result is achieved by cold granulation of a chewing-gum mixture, following by spontaneous adhesion by heating of the granulate. A chewing gum which contains bubbles and which cannot be mixed with other ingredients is thus obtained.
WO 99/2503 describes a process which provides for the preparation of a chewing-gum mass in powder form in which the basic gum is cooled to a temperature of between 0 and −35° C.; the mass thus cooled is then granulated, supplemented with the necessary additives and active ingredients, and then compressed.
U.S. Pat. No. 4,588,592 describes a method of preparing chewing gums containing from 70 to 95% by weight of granulated sugar. The granulated sugar, previously heated to a temperature of between 51 and 93° C., is mixed with the basic gum at a temperature of between 54 and 121° C. The product thus obtained can then be used as it is or transformed into a granular product, after cooling to a temperature of between −6 and −40° C.
U.S. Pat. No. 4,161,544 describes a method of preparing chewing gum which provides for sugars to be mixed with a basic gum, heated to a temperature of 60-120° C.; the temperature is then reduced to between 30 and −5° C. and the mass thus obtained is granulated. The method in question provides for the use of “bulking agents” such as gum arabic, pectin, or other similar additives; as is well known, these ingredients are soluble in water and, as such, will be ingested after brief chewing, together with the sugars, thus leaving a bolus of harder consistency; the object proposed is thus achieved only partially, providing chewing which is extremely variable over time.
Finally, International patent application WO 01/19206 describes a particularly laborious method of preparing chewing gum, requiring a pretreatment of the basic gum mixture which is reduced to pellets of relatively small particles which in turn are then cooled to extremely low temperatures, i.e. below −40° C., by the addition of dry ice. Even when operation takes place in special, greatly dehumidified environments (with consequent greater economic expense and reduced practicality), this selection easily leads to the formation and accumulation of condensation on the dry ice intimately mixed with the gum composition, with the formation of lumps and agglutinations.
As mentioned above, however, the methods described in the above-mentioned patent documents have considerable drawbacks such as, for example, the production of chewing gum with poor chewability.